Parallel holographic encoding modulation method

Abstract

The application provides a parallel holographic encoding modulation method, which comprises the following steps: splitting a laser beam by using a beam splitter to form a first light beam and a second light beam; modulating the first light beam by using a first spatial light modulator loaded with a first hologram to form a first modulated light beam; jointly processing the second light beam by using a second spatial light modulator loaded with a second hologram and a half glass to form a second modulated light beam whose polarization direction is perpendicular to the polarization direction of the first modulated light beam; combining the first modulated light beam and the second modulated light beam to form a writing light beam; and writing storage information on a target storage medium by using the writing light beam. The parallel holographic encoding modulation method can write data points of all polarization states page by page, and can effectively improve the writing efficiency.

Description

Technical Field

[0001] This invention relates to the field of 5D optical storage technology, and in particular to a parallel holographic coding modulation method. Background Technology

[0002] 5D optical storage technology in transparent materials achieves high-density, long-lifetime data storage by directly writing subwavelength-scale permanent nanovoxels into transparent media such as silica, offering a unique advantage of integrated "read-write-storage." Femtosecond laser writing technology is a crucial component of this technology, its core being the simultaneous encoding of intensity information and polarization state using a high-quality laser beam to enhance the information carrying capacity of a single voxel. For example, existing femtosecond writing systems can achieve four linear polarization states (0°, 45°, 90°, and 135°) and generate various encoded states by combining different pulse widths, thereby increasing the storage bits per voxel. However, with the ever-increasing demand for higher data density and faster writing speeds, relying solely on traditional polarization modulation methods is no longer sufficient to meet application requirements. Summary of the Invention

[0003] The parallel holographic coding modulation method provided by this invention can write all polarization state data points page by page, which can effectively improve the writing efficiency.

[0004] This invention provides a parallel holographic coding and modulation method, the method comprising:

[0005] The laser beam is split using a beam splitter to form a first beam and a second beam;

[0006] The first beam is modulated using a first spatial light modulator loaded with a first hologram to form a first modulated beam.

[0007] The second beam is processed by a second spatial light modulator loaded with a second hologram and a half glass plate to form a second modulated beam whose polarization direction is perpendicular to the polarization direction of the first modulated beam.

[0008] The first modulation beam and the second modulation beam are combined to form a write beam;

[0009] The write beam is used to write storage information onto the target storage medium.

[0010] Optionally, prior to the step of splitting the laser beam using a beam splitter to form a first beam and a second beam, the method includes:

[0011] The laser beam is expanded and collimated to increase its diameter to a first preset size;

[0012] The laser beam is purified using a linear polarizer to remove stray polarization.

[0013] Optionally, splitting the laser beam using a beam splitter to form a first beam and a second beam includes:

[0014] The laser beam is split using a non-polarized 50:50 cubic beam splitter to form a first beam and a second beam with the same polarization state and optical path.

[0015] Optionally, modulating the first beam using a first spatial light modulator loaded with a first hologram includes:

[0016] The target data to be written is converted into the corresponding optical polarization state, and the optical polarization state is decomposed to obtain the polarization state of the target data to be written in the first direction.

[0017] Based on the polarization state in the first direction, a first hologram modulating the laser beam in the first direction is determined;

[0018] A first hologram is loaded into a first spatial light modulator, and the first light beam is modulated using the first spatial light modulator.

[0019] Optionally, the joint processing of the second beam using a second spatial light modulator loaded with a second hologram and a half-glass slide includes:

[0020] The target data is converted into the corresponding optical polarization state, and the optical polarization state is decomposed to obtain the polarization state of the target data in the second direction.

[0021] Based on the polarization state in the second direction, a second hologram modulated by the laser beam in the second direction is determined;

[0022] A second hologram is loaded into a second spatial light modulator, and the second beam is modulated using the second spatial light modulator.

[0023] The modulated second beam is processed using a zero-order half-glass plate to smoothly rotate the modulated second beam 90° in the plane, forming a second modulated beam whose polarization direction is perpendicular to that of the first modulated beam.

[0024] Optionally, the joint processing of the second beam using a second spatial light modulator loaded with a second hologram and a half-glass slide includes:

[0025] The target data is converted into the corresponding optical polarization state, and the optical polarization state is decomposed to obtain the polarization state of the target data in the second direction.

[0026] Based on the polarization state in the second direction, a second hologram modulated by the laser beam in the second direction is determined;

[0027] The second beam is processed using a zero-order half-glass slide to allow the second beam to rotate smoothly 90° in the plane;

[0028] A second hologram is loaded into a second spatial light modulator, and the second spatial light modulator is used to modulate the rotated second beam to form a second modulated beam whose polarization direction is perpendicular to the polarization direction of the first modulated beam.

[0029] Optionally, combining the first modulated beam and the second modulated beam to form the writing beam includes:

[0030] The first and second modulated beams are processed by Fourier lenses and then irradiated onto the beam combiner to form a write beam.

[0031] Optionally, after the step of combining the first modulated beam and the second modulated beam to form the writing beam, the method further includes:

[0032] Spatial filtering is applied to the writing beam to improve its optical field quality.

[0033] Optionally, the step of writing storage information onto the target storage medium using a write beam includes:

[0034] A four-fold focal length imaging system using biconvex lenses focuses the writing beam onto the storage medium to write to the target storage medium.

[0035] Optionally, the four-times focal length imaging system using biconvex lenses focuses the write beam onto the storage medium by:

[0036] In the four-times focal length imaging system, a spatial filter is used on the focal plane of the front convex lens to remove the zero-order information and sidelobe stray components of the written beam.

[0037] In the technical solution provided by this invention, a first spatial light modulator and a second spatial light modulator are used to load holograms, which are then modulated onto two orthogonal laser beams. The resulting hologram is then generated by beam combining and written to the target storage medium. Since each point in the hologram carries different phase information, the first spatial light modulator can control the amplitude of each point in the final hologram in the polarization direction by controlling the phase of each point in the first modulated beam. Similarly, the second spatial light modulator can control the amplitude of each point in the final hologram in the polarization direction by controlling the phase of each point in the second modulated beam. By controlling the amplitude of the components of each point in the two orthogonal directions, the polarization direction of each point can be controlled. Therefore, during writing, page-by-page writing to the target storage medium can be achieved using the hologram, effectively improving writing efficiency. Attached Figure Description

[0038] Figure 1 This is a flowchart of a parallel holographic coding and modulation method according to an embodiment of the present invention;

[0039] Figure 2 This is a schematic diagram of the optical path of another embodiment of the parallel holographic coding modulation method of the present invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] This invention provides a parallel holographic coding and modulation method, such as... Figure 1 As shown, the method includes:

[0042] The laser beam is split using a beam splitter to form a first beam and a second beam;

[0043] In some embodiments, the split laser beam should have a single polarization direction, and after splitting, the first beam and the second beam have the same polarization state.

[0044] The first beam is modulated using a first spatial light modulator loaded with a first hologram to form a first modulated beam.

[0045] In some embodiments, when the first spatial light modulator loads the first hologram, taking the first beam as longitudinally polarized as an example, the first hologram should be a hologram corresponding to the phase of the longitudinal polarization, thereby controlling the amplitude of the first beam when it is finally written in the longitudinal polarization.

[0046] The second beam is processed by a second spatial light modulator loaded with a second hologram and a half glass plate to form a second modulated beam whose polarization direction is perpendicular to the polarization direction of the first modulated beam.

[0047] In some embodiments, when a second hologram is loaded onto the second spatial light modulator, taking the second beam as longitudinally polarized as an example, since the second beam has the same polarization state as the first beam, and during final writing, the amplitudes of the longitudinal polarization component and the transverse polarization component need to be controlled simultaneously to control the polarization direction of the vector light. Therefore, a half-wave plate can be used to pre-adjust the second beam to convert it to transverse polarization. In this case, the second hologram should be a hologram corresponding to the phase modulation of transverse polarization, thereby controlling the amplitude of the longitudinally polarized second beam during final writing. As another preferred embodiment, the second hologram can also be a hologram corresponding to the phase modulation of transverse polarization. After the second beam is modulated by the second hologram, it is then processed by a half-wave plate to convert its polarization direction to transverse, thereby controlling the amplitude of the transversely polarized second beam during final writing.

[0048] The first modulation beam and the second modulation beam are combined to form a write beam;

[0049] In some embodiments, the first modulated beam and the second modulated beam are polarized beams that have been phase modulated in two orthogonal directions. Combining the first and second modulated beams can form a vector beam synthesized from the first and second modulated beams as components in two orthogonal directions. The polarization direction of the vector beam is determined by the amplitudes of the first and second modulated beams at corresponding positions.

[0050] The write beam is used to write storage information onto the target storage medium.

[0051] In some embodiments, both the first and second modulation beams are holographic beams formed after holographic modulation. After beam combining, a hologram is formed in which each point is modulated to a specific polarization state. Therefore, during the writing process, the size of the hologram can be used as the writing range, and all voxels within the range can be written at once, which can effectively improve the writing efficiency. Since this embodiment writes data points of different polarization states of all points simultaneously page by page, it significantly reduces the number of times the glass storage medium platform moves, reduces mechanical movement delay, and thus greatly improves the overall data writing rate. This page-based writing method effectively avoids the time overhead caused by point-by-point movement.

[0052] In the technical solution provided by this invention, a first spatial light modulator and a second spatial light modulator are used to load holograms and modulate two orthogonal laser beams. The resulting hologram is then generated by beam combining and written to the target storage medium. Since each point in the hologram carries different phase information, the first spatial light modulator can control the amplitude of each point in the final hologram in the polarization direction by controlling the phase of each point in the first modulated beam. Similarly, the second spatial light modulator can control the amplitude of each point in the final hologram in the polarization direction by controlling the phase of each point in the second modulated beam. By controlling the amplitude of the components of each point in the two orthogonal directions, the polarization direction of each point can be controlled. Therefore, during writing, page-by-page writing to the target storage medium can be achieved using the hologram, effectively improving writing efficiency. Furthermore, this invention, by updating and calculating the hologram on the spatial light modulator, enables arbitrary switching and dynamic adjustment of the output light field polarization state and holographic pattern. Since polarization control relies entirely on a high-speed spatial light modulator, its state switching speed is limited only by the device refresh rate (approximately 60–100 Hz). Therefore, the system can quickly switch to different polarization states and patterns as needed, exhibiting excellent flexibility and practicality.

[0053] As an optional implementation method, such as Figure 2 As shown, prior to the step of splitting the laser beam using a beam splitter to form a first beam and a second beam, the method includes:

[0054] The laser beam is expanded and collimated to increase its diameter to a first preset size;

[0055] The laser beam is purified using a linear polarizer to remove stray polarization.

[0056] In some embodiments, the laser beam may be a high-coherence 633nm single-longitudinal-mode semiconductor laser (0.3mW, horizontally linearly polarized output) as the light source. The laser beam first passes through a biconvex lens (the first lens has a focal length of 30mm and the second lens has a focal length of 150mm) to expand and collimate the original laser beam with a diameter of approximately 3mm to a diameter greater than 10mm, thereby increasing the spatial bandwidth product and ensuring the modulation region width of the subsequent spatial light modulator. The expanded laser beam is then purified by a linear polarizer, allowing only the horizontal polarization component to pass through, thus removing stray polarization.

[0057] As an optional implementation, the step of splitting the laser beam using a beam splitter to form a first beam and a second beam includes:

[0058] The laser beam is split using a non-polarized 50:50 cubic beam splitter to form a first beam and a second beam with the same polarization state and optical path.

[0059] In some embodiments, when splitting the laser beam, for example, a non-polarized 50:50 cubic beam splitter can be used to split it into two beams with equal intensity: a first spatial light modulator SLM_H that enters longitudinal polarization modulation and a second spatial light modulator SLM_V that enters transverse polarization modulation, maintaining a high degree of consistency in polarization state and optical path between the two beams. SLM_H can, for example, correspond to the first beam, and SLM_V can, for example, correspond to the second beam; or, for example, SLM_H can, for example, correspond to the second beam, and SLM_V can, for example, correspond to the first beam.

[0060] As an optional implementation, modulating the first beam using a first spatial light modulator loaded with a first hologram includes:

[0061] The target data to be written is converted into the corresponding optical polarization state, and the optical polarization state is decomposed to obtain the polarization state of the target data to be written in the first direction.

[0062] Based on the polarization state in the first direction, a first hologram modulating the laser beam in the first direction is determined;

[0063] A first hologram is loaded into a first spatial light modulator, and the first light beam is modulated using the first spatial light modulator.

[0064] In some embodiments, the first spatial light modulator can be, for example, a phase-type spatial light modulator (1920×1080px, 5.3µm pixel pitch, grayscale levels 0–255). Each modulator loads a computer-generated hologram (CGH) pre-calculated by the control system based on the Gerchberg–Saxton algorithm. By precisely controlling the diffraction efficiency through phase depth, independent phase encoding and amplitude modulation of the corresponding polarized beams are achieved. When calculating the hologram, the polarization state at each position needs to be determined based on the target data, and the polarization state is decomposed to determine the target phase that the first spatial light modulator should adjust at each position of the first beam, thereby determining the first hologram. In some preferred embodiments, the linearly polarized light generated by the laser can be represented by a Jones vector. .in, For the laser beam in The polarization vector of the position. The amplitude of the laser beam. Let be the polarization direction vector. When the first beam corresponds to SLM_H, the optical field output by SLM_H is: ,in, For SLM_H in Phase function of position, The imaginary unit, is the amplitude coefficient of the first modulated beam in the first polarization direction.

[0065] As an optional implementation, the joint processing of the second beam using a second spatial light modulator loaded with a second hologram and a half-glass slide includes:

[0066] The target data is converted into the corresponding optical polarization state, and the optical polarization state is decomposed to obtain the polarization state of the target data in the second direction.

[0067] Based on the polarization state in the second direction, a second hologram modulated by the laser beam in the second direction is determined;

[0068] A second hologram is loaded into a second spatial light modulator, and the second beam is modulated using the second spatial light modulator.

[0069] The modulated second beam is processed using a zero-order half-glass plate to smoothly rotate the modulated second beam 90° in the plane, forming a second modulated beam whose polarization direction is perpendicular to that of the first modulated beam.

[0070] In some embodiments, the second spatial light modulator can be, for example, a phase-type spatial light modulator (1920×1080px, 5.3µm pixel pitch, grayscale levels 0–255). Each modulator loads a computer-generated hologram (CGH) pre-calculated by the control system based on the Gerchberg–Saxton algorithm. By precisely controlling the diffraction efficiency through phase depth, independent phase encoding and amplitude modulation of the corresponding polarized beams are achieved. When calculating the hologram, the polarization state at each position needs to be determined based on the target data, and the polarization state is decomposed to determine the target phase that the second spatial light modulator should adjust at each position of the second beam, thereby determining the second hologram. In some preferred embodiments, the linearly polarized light generated by the laser can be represented by a Jones vector. .in, For the laser beam in The polarization vector of the position. The amplitude of the laser beam. Let be the polarization direction vector. When the second beam corresponds to SLM_V, and SLM_V is used alone to process the second beam, the optical field output by SLM_V is: ,in, For SLM_V in Phase function of position, The imaginary unit, Let be the amplitude coefficient of the second modulated beam in the second polarization direction. When the second beam enters a half-wave plate (HWP) with a 45° orientation alone, the Jones matrix of the beam after passing through the half-wave plate is as follows:

[0071]

[0072] Where θ is the orientation angle of the half-wave plate.

[0073] Since the second beam needs to be processed jointly by the second spatial light modulator and the half-wave plate, the optical field matrix of the second modulated beam is as follows:

[0074]

[0075] in, For SLM_V in Phase function of position, The imaginary unit, θ is the amplitude coefficient of the second modulated beam in the second polarization direction, and θ is the orientation angle of the half-wave plate.

[0076] As an optional implementation, the joint processing of the second beam using a second spatial light modulator loaded with a second hologram and a half-glass slide includes:

[0077] The target data is converted into the corresponding optical polarization state, and the optical polarization state is decomposed to obtain the polarization state of the target data in the second direction.

[0078] Based on the polarization state in the second direction, a second hologram modulated by the laser beam in the second direction is determined;

[0079] The second beam is processed using a zero-order half-glass slide to allow the second beam to rotate smoothly 90° in the plane;

[0080] A second hologram is loaded into a second spatial light modulator, and the second spatial light modulator is used to modulate the rotated second beam to form a second modulated beam whose polarization direction is perpendicular to the polarization direction of the first modulated beam.

[0081] In some embodiments, during the processing of the second beam by the half-wave plate and the second spatial light modulator, the polarization direction of the second beam can be changed first using the half-wave plate, and then the second spatial light modulator can be used to process the second beam; alternatively, the second spatial light modulator can be used first to process the second beam, and then the half-wave plate can be used to change its polarization direction. The specific optical field matrix can be found in the aforementioned optical field matrix formula. It should be understood that the second hologram used in the processing method where the half-wave plate is used first and the second hologram used in the processing method where the half-wave plate is used later have a transpose-corresponding relationship.

[0082] As an optional implementation, continue as follows Figure 2 As shown, combining the first modulation beam and the second modulation beam to form the writing beam includes:

[0083] The first and second modulated beams are processed by Fourier lenses and then irradiated onto the beam combiner to form a write beam.

[0084] In some embodiments, the SLM_H channel still maintains horizontal polarization output. The SLM_V channel has been switched to vertical polarization output by the half-wave plate. In a polarizing beam combiner, two orthogonally polarized light fields... and The vector light field obtained by superimposing and merging these elements in space and writing the beam can be written as:

[0085]

[0086] At this point, the two components are in phase synchronization, and the linear polarization angle of the vector light field is determined by the amplitude ratio. : Decision, satisfaction

[0087]

[0088] Where α is the polarization angle of the vector light field of the written beam. Therefore, it can be seen that by adjusting the phase functions of the first spatial light modulator and the second spatial light modulator... The encoding depth can be precisely controlled. and The relative intensity of the beams is determined by the polarization angle of the light beams, resulting in a vector light field with arbitrary linear polarization angles after beam combining, representing the polarization state of the written beam at any position. Based on the foregoing, this embodiment effectively improves the writing density by flexibly adjusting the arbitrary linear polarization angle, significantly increasing the number of coded states for a single voxel and substantially increasing data storage density. For example, using four linear polarization angles (0°, 45°, 90°, 135°) combined with two laser pulse durations can generate eight different coded states, storing information equivalent to 3 bits. As the number of available polarization states further increases, the effective number of bits that each voxel can carry will increase proportionally, thereby greatly expanding the data storage capacity in the transparent medium. In some preferred embodiments, a non-polarized beam splitter and a polarization beam combiner are used to spatially superimpose two orthogonally polarized beams in free space, with superposition accuracy required to reach the subwavelength level, ensuring that the output light field has both high-quality holographic image reconstruction and retains the desired polarization state. This beam combining method avoids the destruction of the holographic pattern by fiber coupling, ensuring high-fidelity output.

[0089] As an optional implementation, after the step of combining the first modulated beam and the second modulated beam to form the writing beam, the method further includes:

[0090] Spatial filtering is applied to the writing beam to improve its optical field quality.

[0091] As an optional implementation, the step of writing storage information onto the target storage medium using a write beam includes:

[0092] A four-fold focal length imaging system using biconvex lenses focuses the writing beam onto the storage medium to write to the target storage medium.

[0093] In some embodiments, the vector optical field of the written beam Entering the four-times focal length imaging system. Using the focal length of the first lens as... The focal length of the second lens is For example, the transfer function of a four-fold focal length imaging system is as follows:

[0094]

[0095] The transfer function of a four-fold focal length imaging system, i.e., the spatial frequency transformation process, is represented by the following: The wavelength of the light source, For frequency domain coordinates. This transformation will change the phase function. The corresponding spatial spectrum is mapped onto the intermediate frequency domain plane by the convex lens at the front of the four-fold focal length imaging system, and then focused in reverse by the convex lens at the rear of the four-fold focal length imaging system, realizing the direct "reproduction" of the holographic image used for writing data through phase encoding. Because the four-fold focal length imaging system is compatible with polarization characteristics, the horizontal and vertical polarization components remain orthogonal throughout the frequency domain processing. The light field finally reconstructed on the imaging plane retains the depth information required for encoding the two first and second holograms, and also maintains the correct vector superposition of the two polarization components.

[0096] As an optional implementation, the four-times focal length imaging system using biconvex lenses focuses the write beam onto the storage medium, including:

[0097] In the four-times focal length imaging system, a spatial filter is used on the focal plane of the front convex lens to remove the zero-order information and sidelobe stray components of the written beam.

[0098] In some implementations, after beam combining, the light field enters the four-times focal length imaging system. The zero-order and sidelobe disturbances are removed by the first Fourier lens and the spatial filter, and then the second lens focuses the light onto the image plane to achieve high signal-to-noise ratio reconstruction of the vector hologram. This integrated scheme preserves phase and polarization information.

[0099] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A parallel holographic coding modulation method, characterized in that, The method includes: The laser beam is split using a beam splitter to form a first beam and a second beam; The first beam is modulated using a first spatial light modulator loaded with a first hologram to form a first modulated beam. The second beam is processed by a second spatial light modulator loaded with a second hologram and a half glass plate to form a second modulated beam whose polarization direction is perpendicular to the polarization direction of the first modulated beam. The first modulation beam and the second modulation beam are combined to form a write beam; The write beam is used to write storage information onto the target storage medium.

2. The method according to claim 1, characterized in that, Prior to the step of splitting the laser beam using a beam splitter to form a first beam and a second beam, the method includes: The laser beam is expanded and collimated to increase its diameter to a first preset size; The laser beam is purified using a linear polarizer to remove stray polarization.

3. The method according to claim 1, characterized in that, The step of splitting the laser beam using a beam splitter to form a first beam and a second beam includes: The laser beam is split using a non-polarized 50:50 cubic beam splitter to form a first beam and a second beam with the same polarization state and optical path.

4. The method according to claim 1, characterized in that, The step of modulating the first beam using a first spatial light modulator loaded with a first hologram includes: The target data to be written is converted into the corresponding optical polarization state, and the optical polarization state is decomposed to obtain the polarization state of the target data to be written in the first direction. Based on the polarization state in the first direction, a first hologram modulating the laser beam in the first direction is determined; A first hologram is loaded into a first spatial light modulator, and the first light beam is modulated using the first spatial light modulator.

5. The method according to claim 1, characterized in that, The step of jointly processing the second beam using a second spatial light modulator loaded with a second hologram and a half-glass slide includes: The target data is converted into the corresponding optical polarization state, and the optical polarization state is decomposed to obtain the polarization state of the target data in the second direction. Based on the polarization state in the second direction, a second hologram modulated by the laser beam in the second direction is determined; A second hologram is loaded into a second spatial light modulator, and the second beam is modulated using the second spatial light modulator. The modulated second beam is processed using a zero-order half-glass plate to smoothly rotate the modulated second beam 90° in the plane, forming a second modulated beam whose polarization direction is perpendicular to that of the first modulated beam.

6. The method according to claim 1, characterized in that, The step of jointly processing the second beam using a second spatial light modulator loaded with a second hologram and a half-glass slide includes: The target data is converted into the corresponding optical polarization state, and the optical polarization state is decomposed to obtain the polarization state of the target data in the second direction. Based on the polarization state in the second direction, a second hologram modulated by the laser beam in the second direction is determined; The second beam is processed using a zero-order half-glass slide to allow the second beam to rotate smoothly 90° in the plane; A second hologram is loaded into a second spatial light modulator, and the second spatial light modulator is used to modulate the rotated second beam to form a second modulated beam whose polarization direction is perpendicular to the polarization direction of the first modulated beam.

7. The method according to claim 1, characterized in that, The step of combining the first modulated beam and the second modulated beam to form the writing beam includes: The first and second modulated beams are processed by Fourier lenses and then irradiated onto the beam combiner to form a write beam.

8. The method according to claim 1, characterized in that, After the step of combining the first modulated beam and the second modulated beam to form the write beam, the method further includes: Spatial filtering is applied to the writing beam to improve its optical field quality.

9. The method according to claim 1, characterized in that, The step of writing storage information onto the target storage medium using a write beam includes: A four-fold focal length imaging system using biconvex lenses focuses the writing beam onto the storage medium to write to the target storage medium.

10. The method according to claim 9, characterized in that, The four-times focal length imaging system using biconvex lenses focuses the write beam onto the storage medium, including: In the four-times focal length imaging system, a spatial filter is used on the focal plane of the front convex lens to remove the zero-order information and sidelobe stray components of the written beam.

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